Electrochromic devices include electrochromic materials that are known to change their optical properties, such as coloration, in response to the application of an electrical potential difference, thereby making the device more or less transparent or more or less reflective. Typical electrochromic (“EC”) devices include a counter electrode layer (“CE layer”), an electrochromic material layer (“EC layer”) which is deposited substantially parallel to the counter electrode layer, and an ionically conductive layer (“IC layer) separating the counter electrode layer from the electrochromic layer respectively. In addition, two transparent conductive layers (“TC layers”) respectively are substantially parallel to and in contact with the CE layer and the EC layer. The EC layer, IC layer, and CE layer can be referred to collectively as an EC film stack, EC thin film stack, etc. The EC film stack, and conductive layers on opposite sides of the EC film stack, can be referred to collectively as an “EC stack”.
When an electrical potential difference, also referred to herein as a “electrical potential difference”, is applied across the layered structure of the electrochromic device, such as by connecting the respective TC layers to a low voltage electrical source, ions, which can include Li+ ions stored in the CE layer, flow from the CE layer, through the IC layer and to the EC layer. In addition, electrons flow from the CE layer, around an external circuit including a low voltage electrical source, to the EC layer so as to maintain charge neutrality in the CE layer and the EC layer. The transfer of ions and electrons to the EC layer causes the optical characteristics of the EC layer, and optionally the CE layer in a complementary EC device, to change, thereby changing the coloration and, thus, the transparency of the electrochromic device.
Changes in coloration of a medium, which can include one or more layers, stacks, devices, etc., can be described as changes in “transmission” of the medium. As used herein, transmission refers to the permittance of the passage of electromagnetic (EM) radiation, which can include visible light, through the medium, and a “transmission level” of the medium can refer to a transmittance of the medium. Where a medium changes transmission level, the medium may change from a clear transmission state (“full transmission level”) to a transmission level where a reduced proportion of incident EM radiation passes through the medium. Such a change in transmission level may cause the coloration of the medium to change, the transparency to change, etc. For example, a medium which changes from a full transmission level to a lower transmission level may be observed to become more opaque, darker in coloration, etc.
In some cases, an EC device can switch between separate transmission levels based at least in part upon application of an electrical potential difference, also referred to herein as a voltage difference, across the EC device. Such application, which can include applying one or more separate voltages to one or more separate layers of the EC device, can cause one or more layers of the EC stack, including the EC layer, CE layer, etc. to change coloration, transparency, etc. In some cases, it may be desirable for different regions of an EC stack to change transmission levels differently, so that application of an electrical potential difference across the EC stack causes separate regions of the EC stack to change from to separate ones of two or more different transmission levels.
In some cases, the rate at which one or more portions of an EC stack change transmission level is associated with the temperature of the portions of the EC stack. In order to ensure that an EC stack switches at acceptable speeds, an EC stack can be heated. However, heating an EC stack to ensure such performance of an EC stack can require substantial amounts of electrical power. For example, where an EC stack is required to switch transmission often, the EC stack may be required to remain above a certain temperature, which may require continuous heating of the EC stack, and may further require continuous expenditure of electrical power to enable such continuous heating. In another example, where an EC stack is required to switch transmission on short notice, an EC stack may be required to be heated rapidly, which may require a substantial expenditure of electrical power. Furthermore, in some cases, uniformity of heating of one or more portions of an EC stack is desired.
The various embodiments described herein are susceptible to various modifications and alternative forms. Specific embodiments are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the disclosure to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include,” “including,” and “includes” mean including, but not limited to.